According to the general definition, "polyesters" represent macromolecular substances, which are characterized by the presence of carboxylester groups in the repeating units of the main chains (cf. H. Mark et al., Encyclopedia of Polymer Science and Technology, 2nd ed., Vol. 12, pp. 1-75, J. Wiley-Interscience 1988, R. Vieweg et al., Plastics Handbook, Vol. III, Polyester, Carl Hanser Verlag, 1973, Ulmann's Encyclopadie der Techn. Chemie, 4th ed., Vol. 19, pp. 61-81, Verlag Chemie, 1980). The manufacturing methods serve either self polycondensation of hydroxycarboxylic acids or the polycondensation of dicarboxylic acids with dihydroxy compounds. The former polymers can be reproduced with the general formula ##STR4## where R' stands for a suitable hydrocarbon group; the latter can be reproduced with the general formula ##STR5## where R" stands for a suitable spacing hydrocarbon group; and R"' for the hydrocarbon group of a dicarboxylic acid; and n or n' exhibits in both cases a value corresponding to a molecular weight of the polymer of &gt;10-15.times.10.sup.3. Those polymers in which R" stands for --CH.sub.2).sub.x -- for x=2,4 or 6, have proven to be of particular industrial importance; and specifically those polymers, wherein R" stands for --C.sub.2 H.sub.4 -- and R"' stands for --C.sub.6 H.sub.4 -- (polyethylene terephthalate, PET) and wherein R" stands for --C.sub.4 H.sub.8 -- (polybutylene terephthalate, PBT).
In general the polyalkylene terephthalate can be processed like a thermoplastic in injection moulding or through extrusion. Parts comprising PET are characterized, among other things, by hardness and good abrasion resistance at high dimensional stability.
They exhibit in general a satisfactory impact strength, but only a moderate notch impact strength. Man-made fibers (polyester fibers, abbreviation PES according to DIN 60 001 T1) represent the most important area of application for linear polyesters. In addition, the use of saturated polyesters as injection moulding and extrusion moulding compounds and as film material have gained in importance (cf. Kunststoffe 79, pp. 925-926 (1989).
Therefore, there has been no lack of effort to improve the properties of these bulk plastics, where special stress was laid upon the improvement of the notch impact strength. A large number of patents deal, e.g., with the modification of polyesters by blending them with polyacrylates or through copolymerization of said polyesters.
A large number of patents are applicable to the practical goal of impact modification of polyesters, where one could resort to known ideas. Glass fiber reinforced PET can be blended, for example, advantageously with methacrylate-methyl methacrylate copolymers (JP-A 74 90 345; Chem. Abstr. 82, 99221a). Improved mouldability is claimed, e.g., for blending PET with a (partially) saponified methyl methacrylate-methylacrylate copolymer (cf. JP-A 84 47 256; Chem. Abstr. 101, 131 801 p). The oil resistance of a mixture comprising &gt;50 parts by weight of PMMA and &lt;50 parts by weight of saturated polyester such as PET is underscored in JP-A 84 152 945 (Chem. Abstr. 102, 79 763g). Blending polyalkylene terephthalate with 5-30 wt % of an acrylate graft polymer such as butyl acrylate-methyl methacrylate graft copolymer (cf. DE-A 33 28 568) serves to improve the notch impact strength.
An improvement in the notch impact strength is also achieved according to EP-A 50 265 by blending thermoplastic polyesters with core shell polymerizates, comprising a tough acrylate phase as core and a hard shell comprising PMMA or styrene.
In connection with a silane coupling component, blends of PBT and polyacrylates have, according to EP-A 190 030, good impact strength and extensibility. Observed is a lower moulding temperature.
A blend of PET and polyglycidyl methacrylate and/or fatty acid polyester is known from JP-A 87 149 746 (Chem. Abstr. 108, 7017t). Graft copolymers of tetrahydrofurfuryl esters of (meth)acrylic acid on poly-.alpha.-olefins are also described as additives to polyesters (cf. DE-A 35 25 253). According to JP-A 79 129 050, ethylacrylate-ethylene copolymers represent master batches to incorporate pigments into polyester (Chem. Abstr. 92, 77 480p).
The effect of an addition of PMMA on the crystallization behavior of PET was investigated by V. M. Nadkarny et al. (Polym. Eng. Sci., 1987, 27 (6) 451-457). Practical application as oven-proof pots is projected for crystallizable polyethylene terephthalate, which is modified with 4-29 wt % of a core-shell polymer, for example synthesized from allyl methacrylate butyl acrylate butylene glycol diacrylate as core and polymethyl methacrylate as shell, and with 0-14.5 wt % of polycarbonate (cf. U.S. Pat. No. 4,713,268). Other modification methods avail themselves to an allyl methacrylate-butyl acrylate-methyl acrylate copolymer, on which the methyl methacrylate was grafted (JP-A 82 137 347; Chem. Abstr. 98, 55092k).
The issue concerning polymer compatibility in the blends is not explicity investigated in the prior art, but the indicated applications or the reported flattening effects show that they are incompatible polymer blends.
Thus, in the JP-A 76 75749 (Chem. Abstr. 85, 124 964s) a pearlescence effect for blends comprising, for example 70 parts by weight of PMMA and 30 parts by weight of PBT, is reported. As an index for polymer incompatibility, the reported pearlescence effect for cosmetic containers made of PET and PMMA must also be evaluated (cf. JP-A 82 15929; Chem. Abstr. 96, 200978u). The same also applies to blends of PET and methylacrylate-methyl methacrylate copolymers (cf. JP-A 81 161472; Chem. Abstr. 96, 124179s; JP-A 82 98327, Chem. Abstr. 97, 199245q). With the addition of polyacrylates to polyesters a flattening effect in films is achieved (EP-A 184 028). Even the JP-A 78 133254 (Chem. Abstr. 90, 122 459k) reports about pearlescence effects of blends of acrylate copolymers with acrylonitrile and diene-rubber-graft polymers and aromatic polyesters. For this reason, incompatibility must also be assumed for the iridescent ternary polymer blends comprising PET, polystyrene, and PMMA according to JP-A 80 03 471 (Chem. Abstr. 92, 199 282w).
The impact modification of polybutylene terephthalate plastics, whose heat resistance and weather resistance are shown by D. Rempel in Kunststoffe, 1986, (76), pp. 900-904. Butadiene-styrene-rubbers grafted, for example, with styrene and methyl methacrylate are recommended as impact modifiers (cf. NL-A 73 12 510, DE-A 30 04 942). Similarly investigations were made with acrylate-modified styrene-acrylonitrile copolymers as impact resistant components (e.g., DE-A 27 58 497; JP-A 84 11347, Chem. Abstr. 100, 211063u). In other documents the addition of ethylene-(meth)acrylic acid ester-glycidyl methacrylate copolymers (cf. PCT-Int. Appl. WO 85 03 718) or of ethylene-glycidyl methacrylate-vinyl acetate copolymers (JP-A 78 117 049, Chem. Abstr. 90, 5830j) is reported.
In addition to impact modifiers, polycarbonate is also added as another mix component for polyester (cf. JP-A 76 44160, Chem. Abstr. 85, 47657g; PCT Int. Appl. WP 80 00 972). For fire-proofing, halogen-containing groups, in particular halogenated aromatics, have been introduced into the polymers. Thus, the addition of poly(pentabromobenzyl)acrylates (JP-A 84 06248, Chem. Abstr. 100, 193020w; JP-A 84 20351, Chem. Abstr. 101, 8220w, JP-A 84 20350, Chem. Abstr. 101, 24542h; JP-A 84 11351, Chem. Abstr. 101, 92117j) is recommended. Reference has already been made to the obvious incompatibility (=immiscibility) of polyesters with poly(meth)acrylates. In the case of impact modifiers, the elastomer phase is linked to the polyester phase via the PMMA, or the styrene-MMA-copolymer or via the styrene-acrylonitrile polymer even though there is no compatibility between the polyester and this polymer.
In order to link, reactive components such as glycidyl methacrylate must generally be copolymerized. In the literature miscibility is noted for the systems--poly-ethylene-adipate-PMMA and poly-ethylene sebacinate-PMMA due to the observed depression of the melting point (cf. M. Natov et al., J. Polym. Sci., Part C16, p. 4197 (1968). Also from an industrial point of view, the incompatible blends of polyester with other polymers play the dominant role.